Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Current Conservation of current Batteries Resistance and resistivity Simple circuits Chapter 22 Current and Resistance Topics: Sample question: How can the measurement of an electric current passed through a person’s body allow a determination of the percentage body fat? Slide 22-1

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Derive Capacitance of parallel plate capacitor Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Capacitors Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Note: Battery is a source of constant potential What happens when you pull the plates of a capacitor apart? With a Battery connected With no Battery connected Do the following quantities (a) increase, (b) decrease, or (c) remain the same: Charge E-Field Delta V

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. E field inside a dielectric A dielectric material cannot completely shield its interior from an external electric field, but it does decrease the field. Dielectric Constant κ

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Dielectric Constant With a dielectric between its plates, the capacitance of a parallel-plate capacitor is increased by a factor of the dielectric constant κ: Dielectric strength is the maximum field a dielectric can experience without breaking down.

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Energy Implications of Dielectrics Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Capacitors and Capacitance (Key Equations) Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Capacitance C = |Q| / |Delta V| Property of the conductors and the dielectric Special Case - Parallel Plate Capacitor C = Kappa * Epsilon 0 *A / d Energy Pe e = 1/2 |Q| |Delta V| |Delta V| = Ed

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Uses of capacitors Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Energy Storage Computers/Calculators that maintain memory when batteries are changes Short bursts of energy Camera Flash Difibrilator Short burst high energy experiments Electronic Timing (Analog)

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Reading Quiz 1.The charge carriers in metals are A. electrons B. positrons C. protons D. a mix of protons and electrons Slide 22-2

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Definition of a Current Slide 22-9

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Properties of a Current Slide 22-8

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Simple Circuits The current is determined by the potential difference and the resistance of the wire: Slide I = ∆ V chem R _____

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Light the Bulb Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Can you light a bulb when you have 1 battery 1 Bulb 1 wire A - yes B - no

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Circuit Models for batteries and current Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. These two pairs of possibilities give us four possible models. Battery current outputCurrent character Model 1constant, independent of circuitused up in circuit Model 2constant, independent of circuitconserved Model 3depends on what is in the circuitused up in circuit Model 4depends on what is in the circuitconserved

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Tutorial 1 Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.